Nohochichak

from Wikipedia, the free encyclopedia
Nohochichak
Temporal occurrence
Upper Pleistocene
11,000 years
Locations
Systematics
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Megatherioidea
Megalonychidae
Nohochichak
Scientific name
Nohochichak
McDonald , Chatters & Gaudin , 2017

Nohochichak is an extinct genus of sloth in the Megalonychidae family. It occurred in the late Pleistocene about 11,000 years ago on the Yucatán Peninsulain Mexico . It is documented by a skull with a lower jaw and individual elements of the body skeleton. The findings cameto lightin the Sac Actun cave system, which is flooded with sea water. The sloth representative is one of the largest known members of the Megalonychidae. In contrast to its northern occurrence, it is less closely related to the North American megalonychids such as Megalonyx , but rather it shows closer relationships with the South American family members. Nohochichak probably reached its area of distribution at that time in a late phase of the Great American Fauna Exchange .

features

Nohochichak was a very large representative of the sloth, its size and robustness roughly corresponded to the better-known Megalonyx . However, so far only a partial skull with the lower jaw and individual elements of the musculoskeletal system are occupied. The rostrum and the anterior section of the skull are preserved from the skull, but the posterior part is missing. The rostrum was lower than the rest of the skull, which connects Nohochichak with Australonyx and Megistonyx as well as some Caribbean sloths, but clearly differentiates it from Megalonyx and Ahytherium . In a side view, the snout fell off the frontal bone at a clear angle in the area of ​​the zygomatic arches . Likewise, in contrast to the Megalonyx and Ahytherium , the snout did not widen forward, but remained more or less the same width over the entire length. The width of the rostrum in the front section was about 9 cm, in the rear it was 9.6 cm, the total length of the rostrum obtained was 7.8 cm. When viewed from the front, the nostril had an oval shape with a greater width than the height. Due to the shape of the rostrum, the nasal bone was largely the same width along its entire length; it fused completely laterally with the upper jaw , typical for numerous sloths . On the surface, the nasal bone was slightly arched, the approach to the medial jawbone emerged in a U-shape. On the upper jaw there was an infraorbital foramen above the first molar-like tooth . The zygomatic arch is only known in its anterior section, it was probably not closed, which in turn is a striking difference to Megalonyx and Ahytherium . As with most sloths, the anterior arch section had a descending, an ascending, and a horizontal bony process. The descending extension was shorter than that of Megalonyx and, unlike it, was clearly rounded at the end. In contrast, the ascending appendage was long and narrow. The actual, horizontally rearward-facing arched section began at its base. The palatal bone was straight on the underside of the skull . Only in the front part near the first tooth did it tilt downwards, so that the first tooth was lower than the following teeth.

The lower jaw was 31.7 cm long and has been completely preserved. The spoon-like extension of the symphysis typical of sloths was triangular and short in Nohochichak , it was roughly similar to the extension in Megalonyx . There was a mental foramen at its base . The symphysis itself reached to the front edge of the first molar-like tooth, its total length was 11.1 cm. The lower edge of the horizontal bone body showed a distinct bulge below the molar teeth. The lower jaw measured a total of 9.2 cm in height. This massive protuberance gave the lower jaw a very robust overall shape. The crown process rose up to 12.6 cm, in its shape it was wide and low and rounded. This differs from Megalonyx , Ahytherium and Meizonyx with their rather pointed crown process. In addition, the crown process only marginally protruded from the articular process in Nohochichak . Its articular surface was roughly rotated in relation to the longitudinal axis of the lower jaw. There was a massive angular process on the back of the lower jaw. The mandible foramen sat on the inside at the base of the crown process, while it was formed on the outside in Megalonyx and Meizonyx .

The teeth of Nohochichak showed the teeth typical of sloths consisting of five teeth on each upper jaw and four teeth on each lower jaw, so a total of 18 teeth were formed. As with all Megalonychidae forms, the foremost tooth resembled a canine tooth ( caniniform ), in cross-section it was triangular with rounded corners and a tip oriented towards the rear. He pointed forward at an angle of about 45 degrees. There was a diastema to the rear of the dentition , which extended over a length of 8.8 cm in the upper jaw and 3.1 cm in the lower jaw. In relation to the lower jaw, the length of the diastema was about a quarter of the length of the rear teeth. This is shorter than Megalonyx or some Caribbean forms (30%), but more extensive than Ahytherium (10%). The rear teeth, in turn, were shaped like a molar, characteristic of the sloth . Their outline varied from triangular to oval to rectangular or trapezoidal. In agreement with the other members of the Megalonychidae, the chewing surface was characterized by two transverse ridges ( bilophodont ). The molar-shaped teeth showed hardly any differences in size, but they were extremely high-crowned ( hypsodontal ), which is also indicated by the clear downward bulge of the lower jaw. In relative terms, the high crown surpassed that of Megalonyx . The row of teeth in the lower jaw was 13.2 cm long, of which the molar teeth were 7.8 cm.

Reference

The fossil finds of Nohochichak available to date were found in the Sac Actun cave system in the eastern part of the Yucatán peninsula near the Tulum ruins in the Mexican state of Quintana Roo . The Sac-Actun cave system is one of the largest underwater caves in the world with a length of 220 km. It is sunk into the limestone-rich subsoil of the peninsula and connected to the surface via numerous sinkholes and cenotes . These acted as natural traps for living beings , especially in the Pleistocene , when the cave system was not yet flooded by the low sea water level. The skeletal remains of Nohochichak come from the Hoyo Negro cave. This is a bell-shaped collapse chamber with a 62 m diameter at the base. Its upper edge is 12 m below the current water surface, the bottom is accordingly at a depth of 33 to 48 m below the water surface, in places it reaches up to 55 m. Three passages lead from the chamber to other chambers, which also run 10 to 12 m below the surface of the water. Hoyo Negro was discovered while diving in 2007.

So far, the remains of around two dozen animal species have been detected in Hoyo Negro. The bones are concentrated in the southern section of the chamber. There they form individual clusters that can each be assigned to specific individuals. Numerous long bones are broken. These go back to the fall of the animals into the abyss and the impact on the ground. In extinct forms, in addition to Nohochichak, the sloth Nothrotheriops , the saber-toothed cat Smilodon , the short- snouted bear Arctotherium and the proboscis Cuvieronius could be identified. In addition, there are still some species living today, such as the puma , the Central American tapir and the white-nosed coati . Outstanding is the skull of a female Fund people, called by the nickname "Naia" of an age from 12,900 to 11,750 years BP has and genetically the Paleo-Indians with today's Native Americans connects. The general late Pleistocene age of the finds is further confirmed by radiocarbon dates from Cuvieronius . In Nohochichak's case , a branch was found trapped on the lower jaw, the 14 C age values ​​of which are 11,260 to 11,180 years BP. Studies of the former water level in the Sac-Acton cave system also indicate that the complex was flooded with the global rise in sea level as the glacier melted at the end of the last glacial period . As a result, Hoyo Negro had not been accessible to BP without dry feet for about 8100 years.

Systematics

Internal systematics of the Megalonychidae based on skeletal features according to Stinnesbeck et al. 2020
 Megalonychidae  


 Eucholoeps


   


 Pliometanastes


   

 Pliomorphus


   



 Megalocnus


   

 Parocnus



   

 Neocnus


   

 Acratocnus


   

 Choloepus





   


 Megistonyx


   

 Ahytherium



   


 Nohochichak


   

 Meizonyx


   

 Zacatzontli




   

 Xibalbaonyx







   

 Megalonyx




   

 Megalonychotherium



Template: Klade / Maintenance / Style

Nohochichak is a genus from the extinct family of Megalonychidae within the suborder of the sloths (Folivora) and the suborder of the sibling animals (Xenarthra). The Megalonychidae form a very diverse group, their closest relatives are found in the Megatheriidae and the Nothrotheriidae . The former represent the largest known representatives of the sloth, the latter consist of rather smaller members of the sloth. All three families together form the superfamily of the Megatherioidea . Within the sloth, the Megalonychidae represent a very old line; it was first documented in fossil records in the Oligocene in Patagonia . Its characteristic features include the canine ( canine- shaped ) or incisiform ( incisiform ) design of the front tooth as well as the molar-like ( molar-shaped ) rear teeth. The latter are characterized by two transverse ridges ( bilophodont ) on the chewing surface, which indicates a rather leaf-eating diet of the Megalonychidae. In contrast to the Megatheriidae and the Nothrotheriidae, the rear foot is not rotated, but designed in a plantigradic manner, which means that it retained its original shape. In their phylogenetic past, the Megalonychidae were widespread, they are found in South America as well as in Central America and in North America . The sloths of the West Indies were originally assigned to the Megalonychidae as well as the two-toed sloths ( Choloepus ) that are still alive today . The view is based on skeletal anatomical comparisons. Here, however, molecular genetic and protein-based studies showed that there is no closer relationship between these individual groups.

Due to the often fragmented and incomplete finds, the systematics of the Megalonychidae is complex and has not yet been fully elaborated. However, due to the wealth of shapes, different lines of development can be demonstrated. One is made up of largely South American representatives such as Megistonyx or Ahytherium or Ortotherium , another includes the North American forms Megalonyx and Pliometanastes (as well as Caribbean representatives such as Megalocnus or Neocnus , since they are based on skeletal features ). However, it is currently not possible to determine direct ancestors for the North American representatives of the Megalonychidae. This also means that the connection to the South American forms is rather unknown. According to the first phylogenetic analyzes, Nohochichak is close to other Central American forms such as Meizonyx , which in turn have a closer relationship to South American Megalonychidae. These are more native to the tropical areas of South America. The forms that occur largely in the temperate landscapes of North America, such as Megalonyx or Pliometanastes , on the other hand, represent more distant relatives. Further phylogenetic studies advocate a very close relationship with Xibalbaonyx , another very large late Pleistocene representative of the Megalonychidae from Yucatán and southwest Mexico. The general morphology of the two genera is relatively similar, individual differences affect, for example, the postorbital process , which appears very robust in Nohochichak, but does not occur in Xibalbaonyx or is only weakly developed. Due to the strong similarities, there is a possibility that Nohochichak is identical to Xibalbaonyx and that the deviations that occur are due to species differentiation within a genus, to sexual dimorphism or to pathologies . Since there is too little find material so far, a combination of the two genera has been dispensed with for the time being.

The first scientific description of Nohochichak was carried out by H. Gregory McDonald and research colleagues in 2017. It is based on the finds from Hoyo Negro in Yucatán, the holotype (copy number INAH DP5832) consists of the partial skull and the lower jaw. The generic name Nohochichak is taken from the Maya language and is made up of nohoch for "large" and ich'ak for "claw". It is a reference to Megalonyx , whose name, borrowed from the Greek , also means "big claw". The only species named so far is Nohochichak xibalbahkah . The specific epithet refers to Xibalbá , the underworld in Maya mythology , the word ahkah also has its origin in the Maya language and means "live" or "dwell". In summary, the binomial means "the big claw living in the underworld".

Biogeographical meaning

Nohochichak's discovery indicates that the diversity of sloths outside of South America is higher than originally thought. But it also points to a more complex course of the Great American Fauna Exchange . After the immigration of Megalonyx and Pliometanastes, sloths with more South American characteristics appear to have reached the areas to the north in a possible later wave .

literature

  • H. Gregory McDonald, James C. Chatters and Timothy J. Gaudin: A new genus of megalonychid ground sloth (Mammalia, Xenarthra) from the late Pleistocene of Quintana Roo, Mexico. Journal of Vertebrate Paleontology 37 (3), 2017, p. E1307206 doi: 10.1080 / 02724634.2017.1307206

Individual evidence

  1. ↑ a b c d e f g h i H. Gregory McDonald, James C. Chatters and Timothy J. Gaudin: A new genus of megalonychid ground sloth (Mammalia, Xenarthra) from the late Pleistocene of Quintana Roo, Mexico. Journal of Vertebrate Paleontology 37 (3), 2017, p. E1307206
  2. ↑ Steven E. Fields: Hypsodonty in the Pleistocene Ground Sloth Megalonyx: Closing the "Diastema" of Data. Acta Palaeontologica Polonica 54 (1), 2009, pp. 155-158
  3. ↑ a b c James C. Chatters, Douglas J. Kennett, Yemane Asmerom, Brian M. Kemp, Victor Polyak, Alberto Nava Blank, Patricia A. Beddows, Eduard Reinhardt, Joaquin Arroyo-Cabrales, Deborah A. Bolnick, Ripan S. Malhi, Brendan J. Culleton, Pilar Luna Erreguerena, Dominique Rissolo, Shanti Morell-Hart and Thomas W. Stafford Jr .: Late Pleistocene Human Skeleton and mtDNA Link Paleoamericans and Modern Native Americans. Science 344, 2014, pp. 750-754
  4. ↑ a b c S. V. Collins, EG Reinhardt, D. Rissolo, JC Chatters, A. Nava Blank and P. Luna Erreguerena: Reconstructing water level in Hoyo Negro, Quintana Roo, Mexico, implications for early Paleoamerican and faunal access. Quaternary Science Reviews 124, 2015, pp. 68-83
  5. ↑ Blaine W. Schubert, James. C. Chatters, Joaquin Arroyo-Cabrales, Leopoldo Soibelzon, Jaime J. Awe, Cameron S. Griffith, Guillermo de Anda and Pilar Luna-Erreguerena: The “South American” short-faced bear Arctotherium from the Yucatan Peninsula of Belize and Mexico: implications for their biogeography, paleobiology, and extinction. Journal of Vertebrate Paleontology 36 (suppl.), 2016, p. 220
  6. ^ Sarah R. Stinnesbeck, Wolfgang Stinnesbeck, Eberhard Frey, Jerónimo Avilés Olguín and Arturo González González: Xibalbaonyx exinferis n. Sp. (Megalonychidae), a new Pleistocene ground sloth from the Yucatán Peninsula, Mexico. Historical Biology. An International Journal of Paleobiology, 2020, doi: 10.1080 / 08912963.2020.1754817
  7. ^ Alfredo A. Carlini and Gustavo J. Scillato-Yané: The oldest Megalonychidae (Xenarthra: Tardigrada); phylogenetic relationships and an emended diagnosis of the family. New Yearbook for Geology and Paleontology Abhandlungen 233 (3), 2004, pp. 423–443
  8. ^ A b H. Gregory McDonald and Gerardo de Iuliis: Fossil history of sloths. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 39-55.
  9. ↑ a b Timothy J. Gaudrin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  10. ↑ Frédéric Delsuc, Melanie Kuch, Gillian C. Gibb, Emil Karpinski, Dirk Hackenberger, Paul Szpak, Jorge G. Martínez, Jim I. Mead, H. Gregory McDonald, Ross DE MacPhee, Guillaume Billet, Lionel Hautier and Hendrik N. Poinar : Ancient mitogenomes reveal the evolutionary history and biogeography of sloths. Current Biology 29 (12), 2019, pp. 2031-2042, doi: 10.1016 / j.cub.2019.05.043
  11. ↑ Samantha Presslee, Graham J. Slater, François Pujos, Analía M. Forasiepi, Roman Fischer, Kelly Molloy, Meaghan Mackie, Jesper V. Olsen, Alejandro Kramarz, Matías Taglioretti, Fernando Scaglia, Maximiliano Lezcano, José Luis Lanata, John Southon, Robert Feranec, Jonathan Bloch, Adam Hajduk, Fabiana M. Martin, Rodolfo Salas Gismondi, Marcelo Reguero, Christian de Muizon, Alex Greenwood, Brian T. Chait, Kirsty Penkman, Matthew Collins and Ross DE MacPhee: Palaeoproteomics resolves sloth relationships. Nature Ecology & Evolution 3, 2019, pp. 1121-1130, doi: 10.1038 / s41559-019-0909-z
  12. ↑ H. Gregory McDonald, Ascanio D. Rincón and Timothy J. Gaudin: A new genus of megalonychid sloth (Mammalia, Xenarthra) from the Late Pleistocene (Lujanian) of Sierra de Perija, Zulia State, Venezuela. Journal of Vertebrate Paleontology 33 (5), 2013, pp. 1226-1238
  13. ↑ Sarah R. Stinnesbeck, Eberhard Frey, Jerónimo Avíles Olguín, Wolfgang Stinnesbeck, Patrick Zell, Heinrich Mallison, Arturo González González, Eugenio Aceves Núñez, Adriana Velázquez Morlet, Alejandro Terrazas Mata, Martha Benavente Sanvicente, Fabio Heringoval and Carmen Xibalba Sandovalx oviceps, a new megalonychid ground sloth (Folivora, Xenarthra) from the Late Pleistocene of the Yucatán Peninsula, Mexico, and its paleobiogeographic significance. Paläontologische Zeitschrift 91, 2017, pp. 245–271
  14. ^ Sarah R. Stinnesbeck, Eberhard Frey and Wolfgang Stinnesbeck: New insights on the palaeogeographic distribution of the Late Pleistocene ground sloth genus Xibalbaonyx along the Mesoamerican Corridor. Journal of South American Earth Sciences 85, 2018, pp. 108–120 doi: 10.1016 / j.jsames.2018.05.004